Referring to FIG. 1, there is illustrated a conventional line type luminous device disclosed in Japanese Patent Laid-Open Publication No. 2000-222907.
The line type or line-shaped luminous device 1 includes a light source 2 and a cylindrical light guide 3 having a circular cross-section. The light guide 3 serves to guide light radiated from the light source 2. The line type luminous device 1 further includes at least one reflective layer 4 of a strip-like shape printed on the side of the light guide 3 along a lengthwise direction thereof. Light emanated from the light source 2 enters at one end of the light guide 3 and travels therealong. While traveling, parts of the light are gradually reflected from the reflective layer 4 and emitted through an opposite surface of the reflective layer 4, so that a line type luminous image can be displayed.
Since, however, the light guide 3 is of a cylindrical shape having a convex surface, the light diverges after passing an imaginary focal point thereof to thereby make it difficult to obtain a clear luminous image. Moreover, since the light can be emitted from the whole surface except the reflection layer 4, the light intensity diminishes rapidly as the distance from the light source increases along the light guide 3. Therefore, the difference between the brightness at a point close to the light source and that at a point far away from the light source is too big to make a good display.
Such a luminous device can be used for various purposes and an induction heating cooker is an example of such an equipment that employs a luminous device. The induction heating cooker usually includes an induction heating coil to which a high frequency alternating current is selectively applied. When a pot acting as a load is disposed over the induction heating coil, a high frequency alternating flux is set up within the pot to generate eddy-current circulation therein, thereby causing the Joule heating in the pot itself. Since the pot itself is heated, a heating state or a heating region of the induction heating cooker may not be visibly recognized unlike a gas range or an electric range using a visible heating source such as a gas fire or a red-hot heating coil. Therefore, the induction heating cooker conventionally employs the luminous devices or lamps capable of visually indicating a heating state or a heating region thereof.
Japanese Patent Laid-Open Publication No. 95-312279 discloses such a conventional induction heating cooker employing a luminous device to display a heating region and a heating state thereof. The luminous device of the above-mentioned Japanese Patent includes a multiplicity of first light-emitting diodes (LEDs) arranged around an outer circumference of an induction heating coil of the induction heating cooker. While a current is being applied to the induction heating coil, the first LEDs are simultaneously turned on, so that the heating region can be displayed. Optionally, second LEDs are further arranged around the first LEDs to indicate a heating level of the induction heating cooker.
The above-described induction heating cooker, however, requires a lot of LEDs to fully display the outer circumference of the induction heating coil. With a small number of LEDs, the visual effect of the luminous device may be reduced and the heating region of the induction heating coil may not be clearly identified.
Japanese Patent Laid-Open Publication No. 2001-160483 discloses an alternative conventional luminous device for indicating the heating region and state of an induction heating cooker. In FIG. 2, the luminous device of the above-mentioned Japanese Patent includes a lighting segment 5 having a fan-shaped or a sector-shaped light guide 8 and a light source 6 disposed at a narrow end portion thereof. Disposed at a wide end portion of the light guide 8 is a luminous surface 7. The lighting segment 5 is disposed under an induction heating coil (not shown), and the wide end portion thereof is upwardly bent such that the luminous surface 7 oppositely faces a top plate (not shown) positioned over the induction heating coil.
The lighting segment 5 is assembled with others to make a ring shape along an outer circumference of the induction heating coil. While a current is being applied to the induction heating coil, the assembled lighting segments 5 are turned on in the ring shape to thereby indicate the heating region and state of the induction heating coil. The above-described luminous device, however, costs rather high because of its complicate structure where each lighting segment 5 has a corresponding light source 6 and is assembled with others to make the ring shape.